Restrictions on the levels of hydrocarbons in liquids that may be discharged into navigable and other surface waters, as well as sanitary systems, have become considerably more stringent in recent years. Local, national and international clean water laws have made the typical waste water treatment processes commonly used by ocean vessels and commercial and industrial facilities obsolete by demanding an effectiveness that the commonly used processes are not capable of meeting. In fact, until the introduction of the more restrictive effluent standards, many maritime, commercial and industrial facilities did not need any treatment facilities because their effluent quality was within the parameters of the older standards.
The typical treatment process, if any exists, is a coalescing type gravity separator. These separators depend on the cohesive and adhesive qualities of hydrocarbons and their positive buoyancy. The adhesive qualities of hydrocarbons are used to the treatment system's advantage by either rapid deceleration of the waste stream, a tortuous path, agglomeration of the hydrocarbons on a fibrous material, or a combination of two or more of the above methods. Any of the foregoing methods coalesce small droplets of oil into larger droplets which, if not contaminated with an offsetting negatively buoyant particle, will rise to the top of the treatment tank for removal by skimming. An additional benefit of this type of treatment is that negatively buoyant particulate matter falls to the bottom of the treatment tank as the hydrocarbons rise to the top of the tank. However, neutrally buoyant particulate matter passes through the gravity separator type of treatment facility.
While the gravity type separator has been sufficiently efficient to meet older requirements for liquid hydrocarbon emissions, many designs do not meet the more stringent requirements of today. Additionally, the gravity type separator is only effective on hydrocarbons in their free state. If there is a shift of state to either emulsified or dissolved, the gravity separator has no ability to remove the hydrocarbon contamination because emulsified and dissolved hydrocarbons have little or no buoyancy. The presence of dissolved and emulsified hydrocarbons in the effluent from marine, commercial and industrial activities, as well as free hydrocarbons from untreated waste streams, has become a target for environmental activist groups and is now a violation of local, national and international clean water laws.